Safe to use polystyrene sheet as insulation?

[Dave]

I've got the opportunity to get my hands on a lot of 50mm(?) polystyrene board with a foil coating on one side and am wondering whether to use it as wall/roof insulation in the garage (which is really a workshop and never has a car in it). I tried burning a small sample and it melted, dripped and then burnt with a huge amount of soots. Is this stuff safe to use as intended? The intent would be to fix battens to the walls, fit the polystyrene between them and then plywood over the top; for the ceiling I'd just cut it to fit between the roof trusses and then hardboard over the top.

Dave S

[John Prentice]

Would this insulation touch any electrical cables? If so, I would be wary of using it. Apparently, polystyrene and PVC can react if left in contact with each other for long periods of time. I have read a post elsewhere about an electrical fire that started in somebody's loft after polystyrene broke down the PVC insulation on mains cables, resulting in a short.

Hope that's helpful.

John

[chris French]

In message , John Prentice writes

I'd never heard of such an accident, but it's certainly a possibility.

The expanded polystyrene leaches the plasticisers out of the PVC insulation. however, it's not hard to protect the cables from this, by using, conduit, trunking etc. (in one place I taped polythene sheet round the cable.

[The Natural Philosopher]

I would NOT use it except under screed, personally. Simply because it is a serious fire hazard when it burns. The smoke is toxic, its pretty exothermic, and it reduces visibility due to teh dense smoke it gives off.

OTOH you may well have cans of petrol in plastic cans, in a garage.....

Celotex is arguably far better both insulation and safety wise.

But again, if you line with plasterboard, and seal it properly, maybe the BCO won't have a fit. Why not ask him?

[Ian Stirling]

The smoke isn't very toxic, it's mainly an irritant. That said, enough of it will cause you to expire.

When behind foil coating, it is very hard to ignite.

[chris French]

And this is in a garage/workshop. You aren't likely to be asleep in there when a fire starts, nor (unless you have had an accident that has incapacitated you) if one did start are you going to have difficulty getting out quickly. And presumably the Op is going to clad it in ply or something - otherwise it will rapidly get rather tatty.